1. Field of the Invention
The present invention relates to a method of imaging a liquid-filling container comprising the steps of emitting and irradiating light onto the container by a light emitting unit, receiving the light transmitted through the container by a light receiving unit and imaging the container based on information about the transmitted light. The invention relates also to an apparatus for carrying out the method above, including the light emitting unit and the light receiving unit.
2. Description of the Prior Art
The imaging of a liquid-filling container noted above is employed in a manufacturing line of various beverages such as soft drinks or alcoholic beverages in order to inspect whether the amount of liquid as the beverage filled in a container made of glass or PET is within a predetermined range or not and/or whether any foreign substance is inadvertently mixed in the beverage filled in the container or is present in the container or mixed in the material forming the container.
According to a conventional method of inspecting beverage by way of imaging of a liquid-filling container, a light emitting unit emits and irradiates a visible light having a wavelength of 400 to 700 nm onto the container to be transmitted through the container and this transmitted light is received by a light receiving unit comprising a CCD camera for imaging of the container, so that the inspection is effected based on the image whether the surface level of the liquid inside the container is within a predetermined range or not, and/or whether any foreign substance is mixed in the beverage or is present in the container or in the container material or not.
Such conventional imaging method as above presents no problem when the container or the liquid/beverage contained therein is transparent or nearly transparent. However, the imaging becomes difficult in case the container is a colored container especially of a dark color such as black, dark green or dark brown or the container has a frosted surface treatment, so that the filled amount of the liquid in the container or absence/presence of any foreign substance in the liquid or in the container or container forming material cannot be detected with high reliability.
Namely, if the container has a dark color such as black, dark green or dark brown, as shown in a graph of FIG. 4 (transmittance for a glass thickness of 3 mm), the transmittance of the visible light becomes extremely low. For this reason, when the visible light emitted from the light emitting unit is received by the light receiving unit, the portion of the visible light travelling outside the container is received substantially as it is or directly by the light receiving unit, so that the amount of received light for this area outside the container is large, whereas the amount of light corresponding to the container is extremely small.
Then, since the inspection of the liquid surface of the liquid filled in the container or of the absence/presence of any foreign substance in the liquid or in the container or the container material is to be effected for such area of extremely limited received light amount, the detection error becomes significant or the detection of the liquid surface or mixed foreign substance per se becomes very difficult. Conventionally, this problem has been coped with by increasing the absolute amount of the visible light to be irradiated onto the container. With this method, however, there remains a significant problem in the detection precision.
Further, even if the container per se does not have such dark color as black, dark green or dark brown, if the liquid filled therein has a dark color, then, the detection of foreign substance in the liquid becomes impossible. Moreover, if fine bubbles generated in association with the filling operation of the liquid are present near the liquid surface, the amount of light transmitted through the bubbles will be small due to the effect of diffused reflection of the light by the bubbles and also the amount of light transmitted through the liquid portion will be limited, so that discrimination therebetween is difficult, thus impeding reliable detection of the liquid surface. Also, if the foreign substance is present near the bubbles, the detection of this mixed substance too can become impossible.
The present invention has addressed to such problems of the prior art as described above. A primary object of the present invention is to provide a method and an apparatus for imaging a liquid-filling container which method and apparatus assure reliable detection of the surface of liquid filled in a container or of foreign substance mixed in the liquid or present in the container or the container material not only when the container is transparent, but also when the container is a colored container of a dark color such as black, dark green or dark brown or the container has a frosted surface or when the liquid filled in the container has a dark color.